In the production of electronic parts, such as semiconductor elements, integrated circuits, etc., fine processing techniques by photo-etching are employed. Photo-etching is carried out, for example, by forming a photoresist layer on a silicon single-crystal wafer by spin coating, superposing a photomask having a desired pattern on the resist layer, forming an image by exposure to light, development, rinsing, and the like, and etching the solubilized area to form lines of several microns in width or windows. Precision of the products obtained by the above-described fine processing techniques depends mostly on the properties of the photoresist used, such as resolving power on a support base, sensitivity to radiation, adhesion to a support base, resistance to etching, and the like.
The photoresist includes negatively working resists which are insolubilized upon exposure and positively working resists which are solubilized upon exposure. In general, the negative resists are unsuitable as resists for fine processing due to their poor resolving power, though excellent in sensitivity. On the other hand, the positive resists are excellent in resolving power but inferior in sensitivity or etching resistance and, therefore, improvement of positive resists has been demanded.
Further, with the recent increasing demands for achieving higher densities and higher integration of semiconductor, etc., a process for forming patterns having a line width of 1 .mu.m or less has been studied. According to this process, lithography using radiation of high energy, such as X-rays, an electron beam, an ion beam, etc., is adopted instead of the conventional lithography using light. However, it is difficult with such positively working radiation-sensitive organic high polymer materials used in this process to obtain high sensitivity, though such are excellent in resolving power, as compared with negatively working radiation-sensitive organic high polymer materials.
On the other hand, as the wiring of semiconductor elements, etc., becomes more minute, the conventional wet etching of the base after patterning of a resist layer has been replaced by dry etching. Therefore, resist materials are required to have high resistance to dry etching. However, the conventional resist materials have an essential defect in that attempts to obtain high sensitivities, particularly in the case of positive resist materials, are accompanied by reduction in resistance to dry etching. It has keenly been demanded, therefore, to develop resist materials having improved dry etching resistance.
To this effect, it has recently been discovered that polymers having an ##STR1## bond in the molecule exhibit high resistance to dry etching, particularly with O.sub.2 plasma, and many compounds of this kind have been proposed for use as resist materials as described, e.g., in Japanese Patent Application (OPI) Nos. 141642/82 and 193451/84.
However, sensitivities reached with these resist materials are not always sufficient. These polymers are also disadvantageous in that they are hard to handle in the wafer process due to their low glass transition temperatures and that alkaline aqueous solutions commonly employed for positive photoresists cannot be used in the development.